Hydrogenation process for producing hydroxy acids and lactones



' it carbox'ylic group may be converted to hydroxy from aliphaticdibasic carboxylic acids and esters Patented 1.... 5, i937 .verted,admixing them with hydrogen, and'eon UNITED STATES PATENT oi-"PicsHYDROGENATION PROCESS FOR mDUC- ING HYDROXY, ACIDS AND'LACTONEB Wilbura. Luier, -assignor a E. I. du Pont de Nemours it Company. Wilmington, acorporation Delaware No Drawing. Application September 22, 19:3,

- SerlalNo. 690.56:

This invention relates to a process for the prometals and/or theiroxides at an elevated temduction of hydroxy acids and iactones o1hy'droxy perature and pressure and then suspending the acids. Morespecifically it relates to a process process at such a point that asubstantial porter the catalytic hydrogenation of dibasic acids tionoithe carboxyl groups remain unreduced so and esters of dibasic acidshaving more than one that opportunity is afforded for only one of the 5carbon atom .per carboxyl group, wherein the carboxyiic groups in theoriginal compound to hydrogenation is so controlled as to produoehybereduced to an alcoholic group. droxy'acids and lactones as the majorproducts In the following examples several of the preoi? the reaction.ferr ed embodiments oi! the invention have been This case is acontinuation inpart of appliset forth, but they are presented forpurposes of o cation Serial Number 445,224, filed April 17, 1930illustration and not as limitations. and application Serial Number629,754, filed Ausump I gust 20,1932.

In I copending application Serial Number A hydrogenation catalyst wasprepared as fol- 629,754,15iied August 20, 1932 and U. 8. Patent No.lows: Twenty-three grams of cadmium nitrate, 1s

24 grams of copper nitrate, and 245 grams of 1,839,9'l4issued January 5,1932, there arediszinc nitrate were dissolved in 500 cc. ,oiwater closednew methods for hydrogenating carboxylic acids and esters tor theproduction of and mixed with an equal volume of water convariousalcohols. esters, and other valuable taining iztgramsoi ammoniumbichromate and' products. Further investigation has led to the 75 cc. of28% ammonium hydroxide. After 20 discovery that when dibuic acids and/ortheir stirring, the mixture was exactly neutralized esters arehydrogenated, the procem takes place with additional ammonium hydroxideand aliniairly definite steps and that by suspendingthe lowed to.settle. After several washes by dehydrogenation at substantially themidpoint oi cantation, the precipitate was dried, ignited at thereaction, hydroxy acids and/or lactones of hydroxy acids may beproduced. By this method it is therefore possible to prepareeconomically. polymerizable organic compounds heretofore obtainable onlyby extremely diflicuit and costly steps of organicsynthesis.

This invention has as an object a new and novel process whereby dibasicacids and dibasic esters having more than one carbon atom per suitableior use in'catalyticigas apparatus.

A Twenty-five cc. of the mixed chromite catalyst prepared as above wasloaded into a converter and heated to a temperature 01,380 0. in astream 0! hydrogen. The pressure was maino tained at3000ibs.Dersmiareinchwhilemelted, adipic acid was pumped over the catalyst.Seven hundred and nity-flve gaze. of this acid was pumped through thereaction system in two acids and lactones oi hydroxy. acids. A fin'therobject is to provide a process for obtaining the gen, measured atordinary conditions oi temperacorresponding hydroxy acids and/or'lactones tureandpressure, through the catalyst was 560liters. Analysisof the condensed products showed that a-substantiaiproporiion oi thecarboxyl had survived the hydrogenation do at the high rate 01 flowemployed and a good of aliphatic dibasic carboxyllc acids having morethan one carbon atom per. carboxylic group which may contain assubstituents, aromatic groups.

A still further object is to obtain the above menyield of the We of ,t acapmic acid was timed products by means oi a careiully con- W trolledhydrogenation process. Another-objectm ze g is to carry out the abovementionedp by the use of highly emcient composite hydrogenationcatalysts. Other objects will appear hereinaiter.

' These objects areaccomplished by theioliow-. ing' invention which, inits general aspects, comprises heating the acids and esters to beconl'lite'en hun of copper nitrate on- M solved in. 4 liters oi waterwasmixedwith a solution containing 1000 or onium chromate in an equalvolume oi water. onium hydroxide -was added to neutralise the aciditydeveloped w during precipitation oi the copper onium Thcprecipitate wasfiltered; dried, and ignited at a temperature oi 400 C. after mixtureswith a tactins the Said Wanting tndilute acetic catalyst comprisingeither a simlehydrogenating which it was extraotedtwic metal orits'oxide, era of by acid. The resulting i 1,.

400'- c. and compressed into tablets or grains 25 hours, duringwhlch'tlme the volume of hydro- 35 to powder was i employed forhydrogenation without further treatment. Two hundred fifty grams ofethyl sebacate and 20 grams of copper chromite, prepared as described,were placed in a shaking autoclave. Hydrogen was introduced until thepressure reached 3000 pounds per square inch. The mixture was heated to325 C. and agitated until the-drop in pressure indicated that one halfthe amount of hydrogen needed for complete hydrogenation had beenabsorbed. Separation of the products gave the following results:Fifty-six grams of decamethylene glycol were recovered. One hundredtwenty eight grams of acidic material was recovered from the alkalineliquors. This material was boiled with 450 cc. of glacial acetic acidand cc. of hydrochloric acid. On cooling, crystals separated which werefiltered and then washed with acetic acid. The crystals weighed 51grams. Their melting point was 128 C. to 130 C. The filtrate wasconcentrated invacuo and gave an additional yield of 20 gramsof crystalwhich were washed with benzol and dried, making a total of 71 grams ofthe acetate of u-hydroxydecanoic acid. The filtrate was distilled at 4mm. pressure and gave two fractions. The first weighed 8 grams andboiled at l-185 C., and consisted largely of acetyl w-hydroxydecanoicacid. The second fraction weighed 20 grams and boiled at 185- 210 C. 1

Example 3 Two hundred fifty grams of diethyl hexahydrophthalate and 20grams of copper chromite catalyst, prepared as in Example 2, were placedin a shaking autoclave. Hydrogen was introduced until the pressurereached 3000 lbs. per square inch. The mixture was heated to 265 C. andagitated for 8 hours. Analysis of the crude product for ester contentshowed the presence of 35% of residual ester. On recovery and separationof the products, there was obtained a. 40% yield of hexahydrophthalide(lactone of hexahydro ortho hydroxymethyl benzolc acid).

It is evident from the examples given, that both the batch method andthe continuous method of hydrogenation are applicable to the processesof this invention. The batch method will be preferable when the compoundto be reduced is a solid or very viscous liquid at ordinary temperatureor when the quantities of material to be handled arev small.

Although certain definite conditions of operation, such as time,temperature, pressure, and

rate of fiow of the material to be treated in the presence of thecatalyst, have been indicated in the above examples, it will be apparentthat these factors may be varied within wide limits within the scope ofthe invention. The success of the process depends on the control of thehydrogenation, which may be accomplished in several ways. As thereduction of one carborwl group in each molecule of the compoundprobably takes place before subsequent carboxyl roups are reduced, ascareful adjustment of the time factor will enablesuspension ofthe-hydrogenation in order to permit a maximum yield of hydroxycompound.

Experimentation shows that in most cases, but particularly in the caseof batch hydrogenations,

conditions of equilibrium prevail and may be the determining factor inthe overall carboxyl conversion. Hence an elevated temperature willaffect the equilibrium of the reaction in a direction unfavorable tohigh conversion and so may be used to control the extent ofhydrogenation. similarly, low pressure affects the conversion adverselyand may be employed as a means of obtainingoptimum yields 0! hydroxycompounds. Another method of control is found in the type of catalystused. A catalyst of low activity may be used to retard conversion, withresulting better yields of hydroxy compounds. In the case of continuouslwdrogenation still another method of control may be obtained byadjusting the space velocity of the reducible compound in respect to thecatalyst. A high space velocity will give a shorter time of contact ofthe reducible compound with the catalyst and so enable the conversion tobe controlled.

The preferred temperature for this process is in the range from 200 C.to 450 C., but it is to be understood that the invention is notlimited.to the use of these temperatures, especially when a highertemperature is needed as a controlling factor of the hydrogenation, orwhen other conditions make necessary a variation from the limitsmentioned. The preferred pressure for our process ranges form 1500 to5000 pounds per square inch although the invention is not limited tothese pressures since they may be varied somewhat depending on thecompound to be treated and especially when pressure is used as one ofthe controlling factors of hydrogenation as described above.

When operating by the continuous method, the ratio of hydrogen to theacids and esters may also be varied over a wide range. While it may notalways be strictly necessary, it is preferred to use an excess ofhydrogen, say from 2 to 10 mols per molecular unit of carboxyl groupshydrogenated. However, a low hydrogen ratio may be cited as stillanother means of controlling the amount of hydrogenation.

The quantity of hydrogen absorbed is the best indication of the progressof hydrogenation, and the run should be stopped when one-half thecalculated amount of hydrogen necessary for complete hydrogenation hasbeen absorbed by the compound being hydrogenated. The consumption ofhydrogen may be measured either by the drop in pressure if the hydrogensupply is not directly connected to the autoclave, or by metering thehydrogen consumed when the supply of hydrogen is directly connected tothe autoclave.

An additional method of determining the midpoint of hydrogenation is totake samples of the mixture during hydrogenation. A determination of thesaponification number of the mixture gives an accurate measure of theextent of hydrogenation. However, the data obtained may not beapplicable until subsequent runs are made as considerable, time isconsumed in making determinations of saponification numbers.

Preliminary test runs may be made to obtain the proper time forhalf-hydrogenation for a specific set of operating conditions.

Modifications or combinations of the described methods of control are tobe considered within the scope of this invention.

The rate at which the acids and esters may be passed over the catalystis a function of the molecular weight of the acids and esters and thecatalytic activity of the contact mass. For ordinary compounds such asthose described in the examples, I prefer to pass from 2 to 8 volumesper hour per unit volume of catalyst, but higher rates may be employedto further limit the conversion. 7

The acids and esters may be employed in liquid form or, it they aresolids, may be dissolved in a solvent andthe solution treated as for thepure compounds. Mixtures of acids, mixtures of esters, or mixtures otacids and esters pure state, to obtain these is not a vital factor maybe reduced as well as the individual compounds in a mixtures oi hydroxyacids and their lactones.

silver, copper, tin,,cadmium and lead, andin cerchemical compoundscontaining in which case it is advisable .tain cases iron, cobalt, or

copper catalyst may are, in general, of a basic character. moting oxidesare preferably chosen molybdenum nickel, may be used. Good results areobtained with i'used copper oxide, either wholly or partially reduced.The

promoters such as manganese oxide, zinc oxide, magnesium oxide orchromium oxide. These promoted catalysts may be physical mixtures or 9987. 8-, copper chromate or chromite. A metallic catalyst in the form 01 apowder may'also be used,

to employ a suitable supporting material-such as silica, activatedcarbon, alumina, or a naturally occurring earth such as'kieselguhr. Itmentary nickel supported on kieselguhr and prepared by reduction of thehydroxide or carbonate may be used for the hydrogenation of certainesters, provided a suiiiciently high temperature and pressure are used.Such a catalyst, however,

has the disadvantage that ithas a tendency to carry the hydrogenationcompletely to hydrocarbons rather than to the more desirable alcoholicintermediate compounds.

Certain metallic oxides belonging to the class known, as diiiicultlyreducible oxides and having both hydrogenating and dehydrogenatingpropensities may be employed. By the term difflcultly reducible is meantthat the oxides are not substantially reduced to metal byprolonged'exposure in a state-oi purity to the action of hydrogen atatmospheric pressure and at a temperature of 400-450 C. Such oxidessuitable for the hydrogenation of esters are zinc oxide manganese oxide,'magnesiumoidde, etc. These oxides may be employed either alone or incom? bination with each other or with other oxides which have apromotingactlon. Preferably the oxide employed as a promoter for thehydrogenating oxide has little activity of itself or is much less activethan the hydrogenating oxide employed with mote the activity of the moreactive oxide. It will be noted that the hydrogenating oxides The prolromthe group consisting of the more acidic oxides of elements selected fromthe periodic table. For example, the oxides oi, chromium, vanadium,ungsten. titanium, and

are suitable promoters for zinc oxide or maganese'oxide. Of these,chromium oxide is preferred, since it inhibits more the tendencytowards-catalyidng destructive side reactions. It has been found tobeadvantageous to use chromium oxide in physical admixture or inchemical combination, e. g., as a-chromate' or chromite, with a largenumber of oxides ordinarily regarded as easily reducible. 'lhe acidicpromoting oxides other than chromium oxide be promoted with oxide hasbeen found that eleit, but it yet serves to iurth'erpro higher groups oithe Y may also be used either in physical admixture in chemicalcombination, e. g., as tumstates, vanadates, molybdates, etc. Thereducible oxides when combined or otherwise associated with chromiumoxides are only partially. reduced'lmder conditions of operation and arefound to be very effective catalysts for the hydrogenation of esters.The oxides of cadmium, copper, tin, and bismuth are all examples ofoxides that may be employed in the more Catalysts consisting 01' bothreduced metals and non-reduced oxides are active eyedthough the reactionis carried out at a temperature above the fusion point of the metal.Such mixed catalysts are conveniently employed initially in the form ofchromates or chromites oi the metals. Basic zinc chromate when partiallyreduced with hydrogen is a suitable catalyst for the hydrogenation ofesters by'vlrtue 0! its high activity and absence of side reactions. Itmay be prepared by treating zinc oxide with chromic acid,-'byprecipitation 01 thezinc salt with an alkalichromate or by diilicultlyreducible iorm.

any other suitable means. Manganese oxidechromium oxide mixtures arealso suitable as well as copper oxide in combination with chromium oxideor other acidic oxides.

In carrying out the hydrogenation of esters 'and acids, one of thecatalysts previously disclosed in co-pending application No. 285,501,flied June 14, 1928- (now PatentNo. 1,857,921, dated May 10, 1932), maybe used. These catalysts are included among those outlined in thepreceding paragraph. A preferred catalyst containing a singlehydrogenating metal oxide may be prepared according to the generalmethod described in U. S. Patents 1,746,782 and 1,746,783. This lattertype of catalyst is prepared by ignition of a-hydrogenatingmetalchromate, or of a hydrogenating metal ammonium chromate, or it may beprepared by reduction by hydrogen oi the said chromates at a temperature,oi' 500 C. or higher. Particularly good results have been obtained inester hydrogenation by preparing a catalyst according to the method ofU. S. Patent 1,746,783

wherein a double ammonium chromate of a hydrogena'ting metal is heatedat about 600 C. to

form a chromite catalyst. As indicated in the examples success hasattended the use of 'mixtures of the chromites .0! two or morehydrogenatin'grmetals. The multiple chromite catalyst compositionsdescribed .in closed in my copending application Serial No. 470,238,flied July 23, 1930 (now Patent No. 1,964,- OOLdated June 26, 1934), areeminently suited to in the present invention. The multiple chromitecatalyst compositiomdescribed in the said copending application maybeprepared by precipitation of a mixture oi chromates from solution byadding an alkali metal chromate to an aqueous solution oha mixture ofhydrogenatins metal salts. temperature treatment with hydrogen. Thepreferred procedure comprises the use of a chromite compositionconsisting substantially of zinc chromite but containing lesserquantities of the chroreducible oxides or reducible oxides in adiiilcultly the examples and dis- 7 followed by snition or by highv ormy above described cessive heating. Unlike certain metal catalysts,

they possess a smalltendency to carry the by drogenation beyond thealcohol stage, for example tothe production of the correspondinghydrocarbon. 4 I

It is desired to make mention of the utility of catalysts containingcopper oxide promoted by chromium oxide either in physical mixture or inchemical combination as copper chromate or copper chromite. Thiscatalyst is particularly useful for liquid phase ester hydrogenationreac tions.

The catalysts described above, in addition to the modifiedcopper-chromium catalysts last mentioned, may be modified or promoted bythe addition of oxides or carbonates of alkali metals or of alkalineearth metals, or of basic compounds of alkali metals or of alkalineearth metals, that is, compounds of these alkali-torming metals withacids which are weaker than the metal hydroxide. Other suitablepromoters are compounds containing an alkali or alkaline earth metalcombined with the acid radical of an oxygen-containing acid, e. 3.,barium chromate. These compounds will all be classified under the termbasic compounds of alkali-forming metals. One tendency of the basicpromoter is to suppress the further hydrogenation to hydrocarbon of theformed alcohol.

It will be apparent from the examples given that the process of ourinvention is applicable to a large group of compounds comprisingmultiple basic carboxylic acids and their esters. v group includes suchacids as citric acid and all phatic dibasic acids having more than onecarbon atom per carbonyl group, such as suecinic, glutaric, adipic,suberic, sebacic. and acids having even a larger number carbon atoms andthe esters of these acids. The process is valuable also for conversionof hydroaromatic multiple basic acids and their esters as typified bysuch compounds as diethyl hexahydrophthalate. moncbutyl camphorate andthe similar group 0! acids in the hydronaphthalene series. The processis also applicable to substituted acids such as tartaric acid. g

The multibasic carboxylic acids and their esters are either naturalproducts or are easily obtainable by well known methods of synthesis.The corresponding hydroxy acids and lactoncs have been extremely rarebecause of the diflicult and costly syntheses required for theirproduct'on. This invention provides apractical and economical method forproducing these compounds, and it may be expected that as a resultprocess these products will find a wider application in many holds 0!technology such as in the manuiacture of picsticizers, drugs, resins.and textile finishing materials.

The above description and are to be construed as illustrative :speciflcexamples only and not as limiting the scope or the. invention. Any

modification of" variation therefrom which conforms to the spirit of theinvention is intended to be included within the scope of the claims.

I claim:

i. A process oi producing hydroxy and This , that the compound accuseslactones which comprises reacting hydrogen and a compound of the type:

bonyl groups being joined to different carbon atoms in R bycarbon-carbon bonds, and where X is a radical of the group consisting ofhydrogen and a hydrocarbon residue of an alcohol, under superatmosphericpressure at a temperature in excess of 206 C. in the presence of ahydrogenation catalyst, and stopping the reaction while a substantialportion of the carboxyl groups remains unreduced, then separating thehydroxy acids and laciones from the reaction product.

2. The process of claim 1, characterized in that the temperature is200-450 C.

3. The process of claim 1, characterized in that the temperature is200-450 C. and the pressure is above 100 atmospheres.

4. The process of claim 1, characterized in that the catalyst is amember of the class consisting of the hydrogenating metals and theiroxides promoted by the presence of a more acidic metal oxide.

5. The process of claim 1, characterized in that the catalyst is amember of the class consisting of the hydrogenating metals and theiroxides promoted by the presence 01 chromium oxide.

ii. The process oi claim 1, characterized in that the compound beingtreated is an ester.

7. The process of claim 1, characterized in that the compound beingtreated is an acid.

8. The process of claim 1. characterized in that X in the compound beingtreated is an alkyl radical.

hydrogen necessary for complete hydrogenation has been absorbed.

12. A process of producing hydroxy acids and lactoncs which comprisesreacting hydrogen and a compound of the type:

c I mbox). in which n is a number greater than 1 and R is anon-aromaticradical which contains at least,

one carbon atom per carboxyl group, the carbonyl groups being joined todiflerent carbon atoms in R by carbon-carbon bonds, and where X is aradical of the group consisting of hydrogen and a hydrocarbon residueoi'an alcohol, at a temperature oi 200 to 350 C. and a pressure of 100to 350 atmospheres in the presence or a mixed chr m il-18, I d stoppinithe reaction while a substantial portion of the carboxyl groups remainsunreduccd, then aeparI-ting'the hydroxy acids and iactones fromthcreaction product.

13. The process or claim 1 characterized in that the temperature is 200to 450 C. and the pressurcis 1500 to 5000 pounds per square inch. 14.The process of claim 1- characterized in being treated is an aliphaticthat "x" in the compound being treated is an catalyst untilapproximately one-half of the I a temperature of 200 to 450 C. sorbed.

7 that X in the compound being treated is an lactones, which comprisesreacting diethyl hexaaoaatss polycarboxylic acid and the reaction iscarried 20. The process oi out at atemperatureo1200to450 C. that R" inthe compound being treated is a 15. The process of claim 1 characterizedin. hydroaromatic radical and. the reaction is carthat the compoundbeing treated is an aliphatic ried out at a temperature of 200 to 450 C.polycarboxylic acid and the reaction is carried 21. The process or claim1 characterized in 5 out at a temperature of 200 to 450 C. and at a thatR" in the compound being treated is a pressure above 100 atmospheres.hydroaromatic radical and the reaction is car- 16. The process of claim1 characterized in that ried out at a temperature 01' 200 to 450 C. andthe compound being treated is an aliphatic polyat a pressure above 100atmospheres. carboxylic acid and the reaction is carried out 22. Theprocess of claim 1 characterized in 10 in the presence of a catalystwhich is a member that R" in the compound being treated is a of theclass consisting of the hydrogenating hydroaromatic radical and thereaction is car-' metals and their oxides, promoted by the presried outin the presence of a catalyst which is a ence of amore acidic metaloxide. member of the class consisting of the hydro- 17. .A process ofproducing hydroxy acids and genating metals and their oxides promoted bylactones, which comprises reacting hydrogen and the presence of a moreacidic metal oxide. adipic acid at a temperature of about 380 C. 28. Aprocess of producing hydroxy acids and and at a pressure-of about 3000pounds per square glycols, which comprises reacting hydrogen and inch inthe presence 01' a catalyst comprising ethyl sebacate at a temperatureof about 325 essentially cadmium, copper, and zinc-chromites. C. and ata pressure of about 3000 pounds per 18. The process 01' claim 1characterized in square inch in the presence of a copper chromite alkylradical and the reaction is carried out at hydrogen needed for completesaturation is ab- 19. The process 01' claim 1 characterized in 24.Aprocess of producing hydroxy acids and alkyl radical and the reactionis carried out in hydrophthalate and hydrogen at a. temperature thepresence of a catalyst which is a member of of about 265 C. and apressure of about 3000 the class consisting of the hydrogenating metalspounds per square inch in the presence of a copand their oxides promotedby the presence of a per chromite catalyst.

more acidic metal oxide. WILBUR A.LAZ1ER.

